1. Technical Field
This disclosure relates generally to an image forming apparatus to form an image using a recording head. The recording head has a nozzle surface disposed in a vertical direction or a direction slanted from the vertical direction, and liquid droplets are ejected in a horizontal direction or a direction slanted from the horizontal direction from nozzles formed in the nozzle surface of the recording head.
2. Description of the Background
One example of related-art image forming apparatuses such as printers, copiers, plotters, facsimile machines, and multifunction devices having two or more of printing, copying, plotting, and facsimile functions is an inkjet recording device employing a liquid ejection recording method. The inkjet recording device includes a recording head that ejects droplets of a recording liquid such as ink onto a sheet of a recording medium while the sheet is conveyed to form an image on the sheet.
Examples of the inkjet recording device include a serial-type image forming apparatus, in which the recording head ejects ink droplets while moving in a main scanning direction to form an image on the sheet as the sheet is moved in a sub-scanning direction perpendicular to the main scanning direction, and a line-type image forming apparatus equipped with a line-type recording head that ejects ink droplets and does so without moving to form an image on the sheet as the sheet is moved in the sub-scanning direction.
One example of an image forming apparatus employing the liquid ejection recording method conveys a recording medium such as a sheet of paper in a vertical direction or a direction slanted from the vertical direction, and the recording head ejects ink droplets in a horizontal direction or a direction slanted from the horizontal direction to the sheet while moving reciprocally back and forth so as to form an image on the sheet. Specifically, the nozzle surface of the recording head in which the nozzles to eject ink droplets are formed is disposed vertically or at a slant from the vertical direction, and the recording head ejects the ink droplets horizontally or at a slant from the horizontal direction. (In other words, the above-described image forming apparatus employs a horizontal ejection method. Herein, the term “horizontal” includes an angular range up to 45° with respect to the horizontal, and the term “vertical” includes an angular range up to 45° from the vertical.)
In order to maintain the recording head in good condition, the image forming apparatus employing the liquid ejection recording method generally uses a maintenance device. The device has a suction cap connected to a suction pump or the like that closely contacts the nozzle surface of the recording head to suck out the ink from the nozzles. In addition, a release unit that releases pressure in the suction cap is also generally provided so as to effectively discharge ink or bubbles remaining in the suction cap after the suction of ink from the nozzles and to prevent pressure from building up within the suction cap.
There are known maintenance devices that: remove the suction cap, which is connected to the release unit, from the nozzle surface while maintaining a negative pressure within the suction cap; release pressure in the suction cap while ink droplets are ejected from the nozzles when the suction of ink from the nozzles is about to end; apply positive pressure to the nozzles during a period of time extending from the end of the suction of ink to the removal of the suction cap from the nozzle surface; or set conditions for preliminary ejection of ink droplets from the nozzles for maintenance based on positions of the nozzles relative to the recording head.
In a case in which multiple nozzle arrays each constructed of nozzles and ejecting ink droplets of a different color are formed in the nozzle surface of the recording head in a full-color image forming apparatus employing the horizontal ejection method described above, when the nozzle surface is capped with a single suction cap to suck out the ink from the nozzles for maintenance, ink of different colors or mixed colors may enter the nozzles upon the suction of ink, thereby causing color mixing during image formation. In addition, because the suction cap is also disposed vertically, ink remaining in the suction cap may drip off upon removal of the suction cap from the nozzle surface of the recording head.